This is very individual.
An acquaintance of mine began to gain a lot of weight during pregnancy. After giving birth, then he continued already by inertia. By the way, doctors told her more than once that this was too much, and scientists often talk about this, since a strong weight gain can damage both the health of the mother and the baby.
There are other examples. The organism will create a certain "reserve" of weight, but the difference is in volume. My sister did not gain much weight during pregnancy and after giving birth calmly dropped the excess, however, she gave herself moderate loads during pregnancy. For example, walking.